TABLE 1. Comparison of the Munson method and the sulphuric acid or wet comoustion 



method (Schryver) . 



1 Wet combustion not made, given to show poor concordance of results. 



Table 2 shows that the results obtained when the precipitates are 

 weighed as stannic oxid (SnO 2 ) are as correct as when the precipitate 

 is dissolved and determined elect rolytically * as tin. Schryver has 

 shown that the wet combustion method gives accurate results and 

 good duplicates. This is also shown by the determinations given in 

 Table 2. However, this method has some very serious practical 

 defects. When tin is to be determined in meat, fish, or sirups, only 

 25 grams of material can be digested in one flask. This necessitates 

 making two digestions in order than an amount can be used which 

 will avoid the great multiplication of the analytical error which 

 would occur if the result were calculated as milligrams per kilogram. 

 Using such small quantities of the sample increases the error of weigh- 

 ing and sampling, and, moreover, limits the amount of work which 

 can be done under ordinary conditions. The flasks have a tendency 

 to break during the digestion, which, together with the foaming of the 

 material, requires constant attention and considerable experience 

 before satisfactory results can be obtained. No attempt was made 

 to determine the amount of tin which could be recovered by the 

 various methods by adding known amounts of soluble tin salts to 

 food, since this would not give conditions analogous to those met in 

 practice. 



TABLE 2. Comparison of results by wet combustion or sulphuric acid method and by 



electrolysis. 

 [Grams of tin per 50 grams of sample.] 



[Cir. 67] 



1 U. S. Dept. Agr., Bureau of Chemistry Bui. 107, Revised, p. 



